The invention relates generally to the processing of photosensitive articles, e.g., photographic sheets.
More particularly, the invention relates to an arrangement for wet processing photosensitive articles.
A conventional arrangement for developing photosensitive articles includes a container which accommodates a processing bath. A rack is removably mounted in the container and comprises several driven rollers which are at least partially immersed in the bath. Each roller defines a nip with at least one other roller and cooperates with such other roller to convey photosensitive articles through the bath. The axes of rotation of the various pairs of cooperating rollers define respective planes, and at least some of these planes are inclined to the horizontal at an angle of 45.degree. or less.
Such an arrangement is known, for instance, from the West German Offenlegungsschrift No. 25 14 594. In this arrangement, sets of three rollers each are disposed one above the other. The rollers of each set are resiliently urged towards one another, and the middle roller functions to transport photosensitive articles downwards as well as upwards.
In the developing arrangements of this type, streaks extending in the direction of transport frequently appear on the developed articles for an indeterminate period of time following immersion of the rack in the bath. These streaks are an indication that development was not uniform across the widths of the articles.
Exhaustive research has now shown that nonuniform development across the width of a photographic material is related to insertion of the rack in the bath. The rack is inserted in the bath by positioning the rack so that the roller axes are parallel to the surface of the bath and then lowering the rack straight into the bath. As the rollers enter the bath, air is trapped in the space defined by the lower surfaces of the rollers, the inner surfaces of the rack and the surface of the bath. Since the liquid pressure increases as the rollers descend through the bath, the air is only partially forced along the undersides and to the lateral faces of the rollers where it can escape. Especially when the rollers are long, very nearly parallel and define very tight nips, small air bubbles tend to remain at various locations along the rollers and subsequently combine to form larger air pockets. When the development process starts, a photosensitive article is conveyed through the nip between cooperating rollers and passes through the air pocket or pockets disposed below such nip. The portions of the article which penetrate the air pockets are thus not wetted by active processing fluid for a certain period of time. On the other hand, the portions of the article next to the air pockets continue to be wetted by the fluid and, particularly at the beginning of the development process, undergo relatively intense development. Although the article is later wetted uniformly, the difference in the intensity of development is not equalized. On negatives, the air pockets manifest themselves as bright streaks. Inasmuch as the air pockets are pushed back-and-forth along the roller axes during the development process, the positions of the streaks may vary across the width of the article.
Due to oxidation of the developer, entrainment by the articles undergoing development and slow lateral movement followed by escape, the quantity of trapped air decreases with increasing developing time. Finally, after periods of up to an hour, the air pockets are dissipated.